HIV-1-seropositive intravenous narcotic addicts and homosexuals develope syndrome of immunologic thrombocytopenic purpura (ITP) which has become part of the AIDS related complex as well as AIDS. This syndrome is associated with markedly elevated plateletbound IgG, IgM, C3C4, circulating immune complexes and anti-F(ab')2 antibodies suggesting an immune complex etiology. Narcotic addict patients unlike homosexuals, also have specific anti-platelet 75 IgG antibody. We have evidence that HIV-1 related ITP is being spread sexually into the heterosexual community by narcotic addicts. We propose to study the mechanism(s) of ITP in both groups of patients and study the risk of heterosexual transmission of HIV-1 via the semen of narcotic addicts. This would be accomplished by; 1) Examining the role of impaired megakaryocytopoiesis in the etiology of the disorder by looking for CD4 receptors on megakaryocytes, looking for HIV-1 or its products in megakaryocytes; looking for anti-HIV-1 antibody or its complexes on megakaryocytes. 2) Searching for anti-idiotype antibody against anti-HIV-1 (gp120) since this could be responsible for impaired resistance to HIV-1 infection; as well as the decreased number and function of helper 14 cells in these patients despite the very low copy number of proviral HIV-1 DNA in these cells (<1/10,000). An anti-idiotype antibody against anti-HIV-1 (gp120) should simulate the HIV-1 (gp120) epitopes and bind to the CD4 receptor. 3) Examining the role of increased peripheral destruction of platelets by determining the specific platelet antigenic determinants for the 7S anti-platelet antibody of narcotic addicts: determining how immune complexes of both groups of patients bind to platelets; determining whether the 7S anti-platelet IgG or immune complexes stimulate the phagocytosis of platelets by monocytes. 4) Measuring reticulo-endothelial function in thrombocytopenic and non-thrombocytopenic HIV-1 seropositibive patients, to determine whether there is a correlation between reticulo-endothelial function and thrombocytopenia. Reticulo-endothelial blockade could explain the absence of thrombocytopenia in patients with elevated platelet IgG, IgM and C3C4. 5) Studying the semen and peripheral blood of narcotic addicts and the peripheral blood of their non-addict spouses or sexual consorts for integrated HIV-1 proviral DNA. This would provide valuable information regarding the infectivity of narcotic addict semen and spread of AIDS into the heterosexual community.